1. Field of the Invention
The present invention relates to an organic acid magnesium salt suitable for forming a magnesium oxide film used as a protective film for a dielectric material in a plasma display panel (PDP) and the like by the coating pyrolysis method.
2. Description of the Related Art
Magnesium oxide films are utilized in a wide range of applications such as protective films for PDPs, insulating films, catalyst films, and surface protective films. Conventionally, films of metal oxide including magnesium oxide are formed by physical film forming methods such as sputtering and vacuum evaporation. With these methods, a uniform, dense and highly crystalline film can be obtained. On the other hand, since the films are formed in a vacuum, a large and complex, and expensive apparatus is necessary. Furthermore, since production is performed in a batch manner, the production efficiency is poor, and the production cost is high.
In contrast to physical film forming methods, the coating pyrolysis method is employed by which a metal oxide film can be formed in a simple process without an expensive and complex apparatus.
In the film formation by the coating pyrolysis method, various compounds of alkaline-earth metals are used. For example, compositions containing the following compounds for forming a metal oxide (magnesium oxide) film are known: MgO particles and a MgO precursor that forms MgO by baking (Japanese Laid-Open Patent Publication Nos. 9-12940 and 9-208851), and an alkoxide of an alkaline-earth metal (e.g., magnesium) (Japanese Laid-Open Patent Publication Nos. 6-162920 and 8-329844).
However, the compositions (coating liquids) for forming a metal oxide film generally have poor temporal stability so that a uniform film cannot be obtained, or only a film having a small thickness can be obtained.
Furthermore, in addition to the above-described magnesium compounds, organic acid magnesium salts are known as compounds that can be contained in a composition used in the coating pyrolysis method. However, in general, organic acid magnesium salts have poor solubility in solvents. For example, when they are formed into a coating liquid using an alcohol solvent, opaqueness may occur or a precipitate may be generated. For this reason, a transparent coating liquid without opaqueness or a precipitate has been studied by using various additives.
For example, in Japanese Laid-Open Patent Publication No. 9-95627, a coating liquid is prepared that contains an organic acid magnesium salt, a polyhydric alcohol acetic acid derivative as a solvent, and an additive such as a thickener. Furthermore, in Japanese Laid-Open Patent Publication No. 9-129141, a coating liquid containing an organic acid magnesium salt, a poyhydric alcohol derivative, an organic acid, an amine, and an additive such as a thickener is prepared. However, there is the drawback that the temporal stability of these coating liquids is insufficient.
As mentioned above, the coating liquid containing an organic acid magnesium salt has the drawback that the coating liquid becomes opaque, when a widely used solvent such as an alcohol solvent or the like is employed, and thus, the coating film becomes opaque or the coating film cannot be formed. Even though a transparent coating liquid is formed by employing the above-mentioned technique, the temporal stability of the coating liquid is insufficient.